Step-down transmissions known from practice, such as dual clutch transmissions, automated manual transmission, manual transmissions or suchlike, are usually made with gearwheels mounted to rotate on a shaft, which engage with other gearwheels connected in a rotationally fixed manner on another shaft, thereby forming so-termed paired gearwheels. By alternate rotationally fixed connection of the gearwheels mounted to rotate on the shaft, the gearwheel pairs can be engaged in the force flow of a step-down transmission by means of appropriate shift elements such as synchronizers, claws, clutches or frictional elements, to produce the various gears of the step-down transmission.
In relation to the shaft on which the gearwheels are mounted to rotate, or loose wheels of a step-down transmission are arranged, the shift elements provided for engaging the gearwheel pairs are actuated mechanically, hydraulically, pneumatically or magnetically from the outside or from inside.
From DE 43 25 964 A1 it is known, in the case of gearwheels that rotate on a shaft, to connect them in a rotationally fixed manner to the shaft by means of a hydraulically actuated shift sleeve. For this, the shift sleeve is supplied with pressure medium that passes through the transmission shaft by hydraulic conduits.
The hydraulic actuation of the shift sleeve provided for fixing the gearwheels made as loose wheels requires, in the axial extension of the shaft, structural space between gearwheels arranged on the shaft and to be actuated, and because of this the reduction of the need for structural space, attempted by actuating from the inside of a transmission shaft outward, is not achieved to the desired extent.
In addition, a piston space associated with the shift sleeve is disadvantageously sealed relative to its surroundings by so-termed contact sealing devices, so that during the movement of the piston relative to the cylinder undesirably large friction forces are produced because of the sometimes high actuation pressures. In turn these friction forces lead to an increase of the actuation forces that have to be applied to actuate the piston. Moreover, the sealing action of a contact seal deteriorates with increasing operating time because of friction, and in some circumstances this compromises the functionality of such control means. In addition, further friction losses occur in the area of lubrication oil inlets provided between a housing and the transmission shaft, for the reasons already stated these are undesired.
From DE 102 06 584 A1 hydraulically actuated shift elements are known by means of which gearwheels mounted to rotate on a shaft can be connected in a rotationally fixed manner to the shaft. The shift elements are actuated by two hydraulic actors located inside the shaft and connected in a rotationally fixed manner to it, both of these actors being supplied with oil by a non-rotating oil supply unit.
Disadvantageously, it is very elaborate and expensive to seal and mount such an oil supply unit relative to its surroundings, and the oil supply unit must be arranged coaxially with respect to the shaft. If several actors are arranged in the shaft and are to be hydraulically actuated, then a complex oil supply and outlet system has to be provided.
Another design, known from DE 102 06 584 A1, comprises two actuators which, when a transmission is operating, have a connection rod that rotates together with the shaft, whose rotation speed is decoupled relative to a non-rotating housing. To actuate the gearwheels, made as loose wheels, both electromagnetic and hydraulic actuators are proposed, such that in each case one shift element is connected by a connection rod to one actor and rotates with the speed of the shaft, whereas a cylinder housing of a piston-cylinder unit is static relative to the shaft and the connection rod.
Owing to the high relative rotational speeds that occur during the operation of a transmission device, between a piston connected to the connection rod and the cylinder housing, either complex and costly sealing of the piston space delimited by the piston and the cylinder housing is necessary, this being affected by friction and wear, or the piston space will be characterized by substantial amounts of leakage that cause large pressure and oil losses.
From DE 102 25 331 A1 a change-under-load transmission with central synchronization is known, in which loose wheels on a transmission shaft can be actuated by a hydraulic actuator actuated hydraulically and arranged at least partially inside the transmission shaft. In the case of this actuator, a connection rod coupled to a piston is connected in a rotationally fixed manner to the shaft, whereas a cylinder housing of the actuator, made as a piston-cylinder unit, is fixed to the housing.
The disadvantage here, however, is that the drive decoupling between the connection rod and the cylinder housing is achieved by a corresponding connection between a piston and the connection rod, for example a slide or roller bearing, and the seal between the piston spaces separated from one another by the piston, which is necessary for proper functionality, is achieved only with considerable cost and complexity.
Thus, the purpose of the present invention is to make available a device for actuating a gearwheel made as a loose wheel of a transmission device, which is characterized by little demand for structural space and whose functionality is ensured with low sealing cost and complexity along with low frictional forces.